Currently-used vehicle-mounted navigation apparatuses make each circuit thereof except circuits for producing a screen display operate continuously in order to enable a navigation display in an instant when starting a navigation function the next time also in an operation mode, such as in a screen display off state or in an audio operation state in an AV mode, other than a navigation mode. Therefore, even while being placed in the screen display off state or using the operation mode other than the navigation mode, i.e., while not using the navigation function, the consumption of each unit is progressing.
It can be guessed that a user who often drives his or her vehicle to travel along the same route in daily life often turns off the screen display or places the navigation apparatus in another operation mode other than the navigation mode when driving the vehicle along a road on the route which he or she fully grasps, the road state and so on being also grasped by the user, because the user does not need any navigation. In such an operating condition, a large gap may occur between the usage time of the navigation function which the user recognizes, and the life of the vehicle-mounted navigation apparatus.
There has been also provided a vehicle-mounted navigation apparatus in which the supply of power to a display device of the navigation apparatus is turned off when a user manipulates an electric power switch, and a CPU controls the supply of the electrical power to an external storage unit which stores map data. The above-mentioned CPU reads map data about an area whose center is at the current position of the vehicle from the external storage unit in turn to capture them into a RAM, and stops the supply of the electrical power to the external storage unit after capturing the map data. The vehicle-mounted navigation apparatus reduces the power consumption of the whole thereof by turning on the power supply of the external storage only at the time of performing the operation of reading map data and turning off the power supply except at that time. During travel of the vehicle, a vehicle-mounted navigation apparatus always performs the supply of electrical power to a system controller comprised of a CPU, a RAM, and soon in order to always estimate the current position of the vehicle (for example, refer to patent reference 1).    [Patent reference 1] JP,10-68627,A (see pages 2 to 3 and FIGS. 1 and 2)
Because conventional vehicle-mounted navigation apparatuses are constructed as mentioned above, they read map data as needed during travel of the vehicle in order to recognize the current position of the vehicle regardless of whether the conventional vehicle-mounted navigation apparatuses are performing a navigation display. A problem is therefore that the consumption of a storage unit used by the navigation function, like a DVD driver, an HDD, or the like, progresses, and the user feels that the life of the vehicle-mounted navigation apparatus is shorter against the use frequency of the navigation apparatus which the user has recognized.
A further problem is that the control operation of turning on the power supply of an external storage unit at the time of reading map data from the external storage unit simply causes frequent repetitions of the on/off switching of the power supply of the external storage unit because the system controller always performs a process of using map data if the vehicle is traveling, and it is therefore difficult to improve the life of the vehicle-mounted navigation apparatus.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide a vehicle-mounted navigation apparatus which, in a screen display off state or when performing an operation based on a function other than navigation, reduces the consumption of a storage unit, such as a relatively short-life DVD driver and a relatively short-life HDD, to increase the longevity of the actual use thereof, and which returns to a navigation display promptly.